In native terrain, the rate at which rainfall reaches the ground surface and the velocity with which it travels with respect to the ground surface is decreased drastically by vegetation. Due to collection of rainwater on trees, grasses, and other vegetation, it can take hours for rainwater to reach the earth's surface subsequent to a storm, as the water collects and travels downward from the vegetation to the earth's surface, where lateral flow of the water is further slowed and distributed by grasses and other vegetation. As a result, the storm water generated by a typical storm infiltrates the earth's surface and is absorbed into the soil, resulting in very little runoff and minimal erosion. In the ground, the absorbed water flows downward through the soil where the water is filtered through the soil by natural, physical, and chemical filtration processes. The naturally-filtered water eventually reaches the water table and becomes part of the ground water supply.
In a man-made environment, such as a city or a suburban residential area, the presence of impervious surfaces over a large portion of the earth renders complete infiltration of storm water impossible. These impervious surfaces include buildings, roadways, and other structures. In addition to blocking infiltration, these impervious surfaces also allow storm water to travel at high velocity. As a result, urban landscapes are susceptible to flooding and erosion absent some means of artificial storm water control.
Historically, municipalities have sought to control storm water using elaborate and expensive storm sewer systems. In such systems, storm water is directed into sewers for transportation to water treatment plants through networks of sewer pipes. The water treatment plants subsequently decontaminate the water before it is returned to the ground water supply. In practice, the volume of storm water directed to water treatment plants has proven impractical in certain circumstances. This is especially true in areas where the population has grown rapidly, and municipalities have been unable to expand the capacity of their water treatment facilities in correspondence with the rate of development.
Efforts have been made to manage storm water without directing the storm water into a sewer system. For example, water retention structures may be utilized to store water and gradually release it to a stream or other natural water feature. Infiltration ponds are formed using porous natural materials that allow storm water to be stored in the infiltration pond and gradually absorb into the ground. Underground water storage structures such as basins, vaults, and drywells provide for water storage and gradual infiltration. However, such structures typically drain water solely near the bottom of the structure, thereby preventing the storm water from naturally filtering through the soil as it travels downward toward the water table.
It would be desirable to have a modular structure that allowed storm water to be stored therein and infiltrate into the surrounding soil down the entire height of the structure.